1. Technical Field
The disclosed embodiments relate in general to methods for manufacturing fences, and in particular to manufacturing fences and fence panels in a factory environment that are tailored for installation at specific pre-determined locations.
2. Description of the Related Art
Fences are ubiquitous in modern society, used in a vast range of applications, to mark and accent boundaries, provide security, and control movement of people and animals. Thousands of miles of new and replacement fences are installed every year in the U.S., and utilize vast amounts of construction related natural resources.
FIG. 1 shows a landscape with a fence 100 extending along portions thereof. The fence 100 shown in FIG. 1 comprises two major segments, or runs 102. A run is a section or portion of a fence that extends between natural dividing points such as corners, gates, buildings, etc. Except where a fence is attached to a building, each run 102 generally has a main post 104a at each end and line posts 104 spaced between the main posts. Each pair of adjacent posts 104 has a fence panel 106 coupled between them. Each panel 106 comprises horizontal elements, or rails 108, and vertical elements, or fence boards 110.
Typically, fence construction and installation involves a number of steps. In some cases, a site survey is done to determine the precise location of the fence and to prevent the all-too-common (and potentially very expensive) occurrence of installing a fence a few inches or feet beyond the actual property line. A contractor visits the site to estimate the materials and labor required to build and install the fence. In addition to simply measuring linear feet required, elements such as topography and obstructions must be reviewed and accounted for. If the fence location has not been marked by the owner or surveyor, the contractor may mark the location during the initial visit, or during a later visit. Installation is scheduled, and materials are ordered and delivered to the site.
Depending on the scope of the project, the locations and spacing of the fence posts may be determined and laid out in advance, by a landscape architect, for example, or left to the installation crew to determine on site. In either case, the spacing of the posts is limited by the material available, and typically is selected to make best use of that material. For example, 96 inch lumber is commonly used to frame wooden fences, so the maximum distance between posts cannot exceed 96 inches. On the other hand, if the contractor uses 96 inch lumber, it would be wasteful to set the posts 60 inches apart, which would result in about three feet of waste from every framing rail. However, because of other considerations, some waste is unavoidable. It is generally preferable to evenly space the posts of a given run of fence, to provide an attractive and unified appearance. Inasmuch as such a run will rarely be evenly divisible by eight feet, each post will be something less than eight feet apart. Additionally, if the terrain includes changes in elevation which the bottom and or top rail must follow, the length of the angled framing rails between two posts that are at different heights may be much greater than the lateral distance between the posts, which reduces the maximum permissible horizontal distance between any of the posts of that run. Furthermore, it can be difficult, or at least time consuming, to precisely position a post to within a fraction of an inch, so a margin of an inch or two is generally provided. Thus, the posts may be spaced anywhere from a couple of inches to a couple of feet less than the maximum allowable distance. Finally, when building fences from natural materials such a wood, it is not uncommon for individual pieces to be unsuitable, because of, for example, a knot in a position that unacceptably weakens a part, or an excessively warped board, etc. For all of these reasons, some material waste is expected and allowed for in the original estimate when calculating the materials for the frame rails, and, for similar reasons, when calculating materials for fence boards and posts.
Once the materials and crew are at the site, and with post locations marked, the post holes are dug, and the posts are installed. Each post hole may be partially backfilled with gravel to improve drainage, and the post is then stood in the hole and held in place by several stakes driven into the ground around the post and braces of scrap lumber nailed to the stakes and the sides of the post. A concrete footing is poured into the hole around the post and allowed to set, and the stakes are later removed. With all the posts in place and the footings set sufficiently to remove the braces, frame rails are cut to fit, and attached to the posts, extending between adjacent posts along the bottom and top of the fence. Fence boards are then cut to length and attached to the frame rails. Perfectly parallel and consistently spaced fence boards along the entire fence run is important, because differences in spacing will become very obvious to an observer when there is daylight behind the fence. Because of variations in the spacing of the posts, it is often necessary to rip fence boards lengthwise to maintain the correct spacing in some of the panels of a fence run. Additionally, the lengths of the fence boards may vary considerably. For example, the ground line between posts can have obstructions or changes in elevation that the installer adjusts for in the length of the fence boards in order to maintain a straight line at the top of the fence while still maintaining proper spacing or ground clearance at the bottom. Additionally, many fences include decorative features along the top, such as arches or waves, in which case the builder may extend the fence boards above the desired finish line, and cut the fence boards to follow the desired shape, after installation. The posts are also cut down to the final length after installation, and post caps or finials are often attached to the tops. After the fence is installed, it is usually painted or stained to protect the wood and extend its useful life.
If properly executed using good quality material, a fence that is built and installed as described above can be very attractive, and can last for many years. However, it will be noted that there is a significant amount of waste that is produced. Not only does such waste result in higher material costs, it increases shipping costs because it must be transported to the site and later removed, it increases landfill use, and fees, and wastes otherwise valuable resources.
In view of the expense, labor, and waste associated with installing a fence that is custom-built on site, another method of building and installing fences has been introduced. Pre-manufactured fence panels are becoming more available, and increasingly can be found in a wide variety of materials, including wood, vinyl, composite, aluminum, steel, concrete etc., and in a wide variety of designs.
Pre-manufactured panels or kits are typically sold from retail lumber and hardware outlets. The panels and kits are provided in standard sizes and are ready for installation. One common panel size, of the many available, is six feet tall by eight feet long. The installer digs the post holes at intervals of eight feet plus the width of a fence post, and places the first post, with stakes and braces to hold it plumb while the concrete sets, as described above. However, the installer also attaches the first fence panel to the post, and may attach the second post to the first panel at the same time, installing both posts together. The installer then progresses post-by-post, attaching a panel between each pair of posts before pouring the footing around the second of the pair, bracing each post and shimming up each panel to ensure that the post is held plumb and the fence level until the post footings are sufficiently hardened, which may be several days because of the mass of the fence being supported. This process ensures that the spacing between the posts is correct for the eight-foot panels. At the end of a fence run, if the last post is less than eight feet from the previous one, the installer cuts a fence panel to fit in the remaining space. Alternatively, the installer may install all of the posts first, but this requires significant care to ensure that the distance between the posts is exactly correct. Otherwise, it may be necessary to trim the panel to fit, or shim the post to fill a gap.
In contrast to site built fencing, pre-manufactured fence panels can be produced efficiently, inexpensively, and at a consistent, predictable quality. Because they are produced in a manufacturing facility, waste can be significantly reduced, and the waste that is produced is more likely to be recycled either internally to produce other products or externally rather than sent to a landfill. Material handling methods and automated machines for material optimization allow utilization of all lengths of raw materials. The factory can obtain lumber that has not been cut to standard lengths, but is the full length of the log, or stem, from which it was milled. Scrap that won't work on one fence panel or design can be diverted and used for another. Flaws and defective lumber can be detected automatically, and can often be cut out, allowing the remaining material to be salvaged. This optimization and defective-material/scrap management process is much more environmentally friendly than site-built fence processes, especially as it relates to reducing the production, and increasing the productive recycling, of waste lumber. As tree trunks don't come in perfect length increments, the factory can bring in material in lengths determined by the actual tree trunks and optimize those random lengths via computer to best utilize the material, and minimize waste. The panels can be primed or finished in spray booths or dip tanks in large volumes, using better quality control, wasting less material, and reducing or eliminating the environmental impact that arises from on-site finishing.
Overall, fences built using pre-manufactured fence panels can be made more efficiently, less expensively, and to higher and more consistent quality standards, with less waste and less environmental impact, than fences custom-built on site.
Optimization systems are commonly used in the lumber industry at various stages between the forest and the finished product, to maximize the yield of salable lumber from each stem. For example, in a sawmill, stems are cut into boards of various thicknesses for curing. After curing, the boards are carried by automatic machinery through a series of scanners of various types, to detect defects such as knots, checks, bow, warp, wane, etc. The system determines where to cut the boards for the best yield according to various criteria. For example, a rough board might be wide enough to cut a 2×12 board from, which, because of some minor knots and wane, would be graded as 2-and-better. However, if cut differently, the same rough board might also yield one 2×6 board of select grade and one 2×4 board of economy grade. If the optimization system is programmed to select for the best financial yield, and if the programmed market value of the 2×12, 2-and-better board is less than the combined market value of the 2×6, select, and 2×4, economy boards, the optimizer system will automatically cut the rough board into the 2×6 and 2×4 boards, which results in more material waste, but more profitability for the mill. On the other hand, if the system is programmed to select for greatest material yield, the system will cut the rough board into the 2×12 size.
Another criterion that is commonly used in the optimization process is length, because the dimensional retail lumber market heavily prefers lengths that are 8 feet and longer, whereas the fence board market prefers 5 and 6 foot long 1×6 nominal fence boards, with a heavy preference for the 6 foot lengths. Most retail outlets offer dimensional lumber, e.g., 2×4, 2×6, and 2×8, in 8, 10, and 12 foot lengths, but do not sell shorter lengths. Even with optimization, sawmills inevitably produce some lumber that is shorter or narrower than these desired lengths or widths. With regards to fence boards, at present, there is some commercial market for 5 foot lengths, but almost none for shorter lengths. Because there is very little market for these “mill shorts,” they are typically scrapped or sold at very low cost.
Some manufacturers of pre-manufactured fence panels have begun to produce fence designs that make greater use of mill shorts in order to exploit the relative abundance and low cost of the material. For example, the panels of the fence 100 of FIG. 1 are of a 6 foot horizontal lattice-top design sold by the Copper River Fence Co., in which most of the fence board material is cut from lengths that are shorter than 5 feet, which is shorter than the typical fence board retail market can effectively stock and sell.